1. Field of the Invention
This invention relates to the application of a heat or photosensitive polymeric material to a printed circuit board, semiconductor wafer, semiconductor lead frame, or electronic packaging.
2. Description of the Prior Art
Prior to electroplating or stripping operations in the manufacture of printed circuit boards, it is the current practice in the art to partially cover the surfaces of the circuit boards or other substrates with a masking tape. The masking tape comprises a foil-like carrier that is made of a material such as paper or plastic and a coating of an adhesive material applied to one side of the carrier, which carrier may be self-adhesive or adhered to the circuit board by a pressure or heat activation process.
Such masking tapes serve the purpose of protecting and thereby preserving intact, during plating and stripping operations, predetermined portions of circuit boards. For example, during the plating of gold on the fingers or edges of a circuit board, the areas, which are not to be stripped of tin/lead and subsequently gold plated, are protected from the stripping and plating baths by a pressure sensitive tape commonly known as "platers tape."
Many problems are encountered in the use of such a tape and tape masking process. These problems include the following:
1. The tape is manually applied. The application of a tape product manually is cumbersome and non-automatable.
2. The tape is hand-stripped or mechanically removed which tends to produce defect-causing "nicks" in the printed circuit board.
3. The residual adhesive usually left behind by the pressure sensitive tape must be removed with an organic solvent. Typically, in printed circuit facilities, several operators are stationed at the end of the gold plating line. Their major function is to manually remove the platers tape and then apply organic solvents in an effort to remove the adhesive residue. Reliability problems may result if all the residue is not removed.
4. The organic solvents required to remove the residual adhesive causes ionic contamination problems on the surface of the circuit board and are possibly hazardous to the health of personnel engaged in the handling thereof. There is a movement in U.S. industry which is lobbying for reducing worker contact with organic solvents like M.E.K., 1,1,1, trichlorethane, industrial alcohols, and methylene chloride because of their potentially adverse health effects.
5. Organic solvents, such as methylene chloride, used to remove the tape residue, can also remove or soften the epoxy resin which is on the surface of the circuit board.
6. Platers tape does not conform well to the circuit trace geometries. As a result, plating and stripping bath chemicals can wick under the tape to cause uneven plating.
7. Plating bath chemicals which wick under the tape can be released in subsequent baths resulting in cross contamination.
8. The adhesive tape process is labor intensive, and therefore, expensive.
Thus, there is a need for improvement in the materials used and the method of their application to predetermined portions of the surfaces of circuit boards, which portions must be protected from the stripping and plating processes associated with gold finger plating. The present invention was devised to fill the gap that has existed in the art in these respects.